For the purpose of realizing a wireless broadband multimedia system for providing a high reliability and a large scale service, an OFDM transmission scheme has been highly regarded since the OFDM transmission scheme allows a signal to be transmitted at a high data rate in a millimeter-wave bandwidth ranging from several GHz to tens of GHz.
The OFDM scheme is one of several frequency multiplex schemes. In the OFDM, data to be transmitted are inverse-Fourier-transformed, and a bandwidth is divided into a plurality of subcarriers to be transmitted; and the transmitted subcarriers are fast-Fourier transformed to transform the subcarriers into the original data in a receiver. Also, a predetermined orthogonal condition is provided to the subcarrier frequencies so as to respectively divide the subcarriers across the spectrum.
Generally, a transmitter of the OFDM system converts data to be transmitted into parallel data, modulates the respective parallel data, performs an inverse-fast Fourier transform of the modulated data, outputs the inverse-fast Fourier transformed data as time domain signals, converts the data into serial signals, and transmits the data.
A receiver then converts the received signals into digital parallel signals, performs a fast-Fourier transform of time-domain data of the parallel data to convert the same into frequency-domain data, estimates a channel estimate of the frequency domain data, and demodulates the data with reference to the channel estimate.
In the OFDM system, when subchannels formed on the time domain which is a symbol axis coexist with subchannels formed on the frequency domain in a frame, the data are allocated for each subchannel in order to perform data burst allocation of the two types of subchannels, and data of a corresponding symbol are mixed according to a subcarrier allocation algorithm. This process is performed by a previous unit of an inverse-Fourier transform unit while using a buffer corresponding to a symbol size.
When the subcarrier allocation to the subchannel formed on the symbol axis is performed for each N number of symbols, a delay corresponding to the N symbols is generated. Accordingly, the delay corresponding to the N symbols affects a system when a carrier allocator for allocating the subchannels for each N number of symbols is applied in the time division duplexing (TDD) scheme.
In addition, when the delay is generated by allocating the subcarrier to subchannel formed on the symbol axis, additional buffers are required such that a time delay corresponding to the above-noted delay may be generated for the subchannel formed on the frequency domain.